Sample dimension measuring method and scanning electron microscope

ABSTRACT

The present invention suppresses decreases in the volumes of the patterns which have been formed on the surfaces of semiconductor samples or of the like, or performs accurate length measurements, irrespective of such decreases. In an electrically charged particle ray apparatus by which the line widths and other length data of the patterns formed on samples are to be measured by scanning the surface of each sample with electrically charged particle rays and detecting the secondary electrons released from the sample, the scanning line interval of said electrically charged particle rays is set so as not to exceed the irradiation density dictated by the physical characteristics of the sample. Or measured length data is calculated from prestored approximation functions.

The present application is a divisional of U.S. application Ser. No.10/450,852, which was the National stage of International ApplicationNo. PCT/JP02/02983, the entire disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of measuring the dimensions ofmicrostructured patterns by use of a scanning electron microscope, andto the scanning electron microscope to be used for the abovemeasurement; the invention relates more particularly to a method inwhich the dimensions of the samples varying in shape are to be measuredby radiating electron beams, and to the scanning electron microscope tobe used for the above measurement.

During the manufacture and inspection of semiconductor devices,thin-film magnetic heads, and other functional element products by useof microstructured surface processing, scanning electron microscopes arecommonly used to measure the widths of processed patterns (hereinafter,this measurement process is referred to as length measurement) and tovisually inspect the patterns.

The conventional scanning type of electron microscope is an apparatusintended to form images of samples, wherein the electron beam that hasbeen emitted from an electron source and dimensionally restricted by aconvergent lens/object lens combination which utilizes the mutual actionbetween a magnetic field or an electric field and the electron beam isapplied to the sample for its one-dimensional or two-dimensionalscanning by use of a deflector, then the secondary signals (secondaryelectron, reflected electron, and electromagnetic wave) that have beengenerated from the sample by the irradiation of the electron beam aredetected using a detector which utilizes a photo-electric effect or thelike, and the detected signals are converted and processed into visiblesignals such as luminance signals synchronized with electron beamscanning of the sample (hereinafter, these signals are referred to as“image signals”).

For the conventional scanning type of electron microscope, efforts areexerted so that the image corresponding to the shape of the sample to beobserved and measured in length can be obtained with high accuracy. Thatis to say, when the surface of a sample is observed,conversion/processing into image signals takes place in a plane areaaccurately analogous to the corresponding scan area (hereinafter, theplane area is referred to as the image area), and the image signals fromthe various points in the scan area are also arranged at positionsaccurately analogous to those of the scan area. This arrangement canusually be implemented by:

1) Making both the scan area and the image area rectangular andconstituting one side of each rectangle as length with the same numberof scanning lines, and

2) Matching the scan area and the image area in terms of the ratiobetween the scanning line length and the scanning line-to-line distance.

Thus, the distance between any two points on the sample surface alwayshas a constant ratio with respect to the distance between thecorresponding two points on the sample image. This ratio is themagnification of the scanning electron microscope. Such an art hasalready been commonly realized as the basic technology for constructinga scanning electron microscope, and this art is described in, forexample, on pages 2 onward of “SCANNING ELECTRON MICROSCOPY”, a writingby L. Reimer, a German scientist.

In addition, the distance between any two points on the sample surfacecan be easily calculated from the thus-obtained sample image. Thiscalculation is generally called “length measurement”, and a scanningelectron microscope having the relevant calculating function is calledthe “length-measuring electron microscope.”

Japanese Application Patent Laid-Open Publication No. 2001-147112, onthe other hand, describes an example in which the scan area on thesample surface and the sample image are not analogous. In this example,in order to dimensionally measure the patterns of a sample thatabsolutely require reduction in magnification because each pattern isspaced in spite of consisting of very small elements, an image of thesample is prolonged in a vertical direction with respect to the straightline connecting any two points on the sample. Thus, a secondary electronimage is formed for improved dimensional measuring accuracy.

SUMMARY OF THE INVENTION

For the conventional scanning electron microscope, an electron beam withan attainable energy level of at least several hundreds of electronvolts is, of course, irradiated onto the surface of the sample to beobserved.

In recent years, the microstructured processing levels of semiconductorsurfaces have been further enhanced and an argon fluoride (ArF)photoresist, which is one type of photoresist reacting to, for example,argon fluoride (ArF) eximer laser light, has come to be used.

It is believed that since the ArF laser beam has a short wavelength of160 nm, the ArF photoresist is suitable for exposure of furthermicrostructured circuit patterns. Through recent closer studies,however, it has come to be known that since the ArF laser beam is verybrittle against electron beam irradiation, when a formed pattern isobserved or measured using a scanning electron microscope, the acrylicresin and other components of the base material will suffer condensationreaction due to the convergent electron beam scan and the resultingdecrease in volume (hereinafter, this event is called “shrinkage”) willchange the shape of the circuit pattern.

For a semiconductor device, the shape and dimensions of its circuitpattern must be strictly managed to achieve the design performance ofthe device, and for this reason, a length-measuring electron microscopecapable of measuring micro-dimensions is used during the inspectionprocess. However, there is the problem that since, during the observingand measuring processes, electron beam irradiation for lengthmeasurement changes the shape of the pattern, the desired circuitpattern design data cannot be obtained and this causes the deteriorationof the device in characteristics and/or its destruction.

There is also the problem that since line width changes, even when thesame dimension is measured, measured data disperses with each measuringoperation and measuring accuracy does not improve. At present, thereexists no apparatus that replaces the length-measuring type of electronmicroscope in that micro-dimensions can be measured with the desiredaccuracy, and the shrinkage of patterns is a major bottleneck in thesemiconductor device manufacture that uses the ArF photoresist. For theconventional type of scanning electron microscope, therefore, noattention is paid to the shrinkage of samples during electron beamirradiation and there has been a problem with the accuracy of measuredpattern dimensional data. Referring again to Japanese Application PatentLaid-Open Publication No. 2001-147112 mentioned earlier in thisSpecification, one can see that although attention is paid to theaccuracy of dimension measurement between any two points distanced onthe sample, no attention is paid to the shrinkage of the sample duringthe irradiation of the electron beam.

The first object of the present invention is to suppress the shrinkageof patterns, which are likely to suffer shrinkage due to electron beamirradiation during measurement, and thus to enable accurate dimensionmeasurement of these patterns.

The second object of the present invention is to enable accuratemeasurement of pattern dimensions, irrespective of whether theirshrinkage occurs.

In order to achieve the above-mentioned first object, by use of ascanning electron microscope equipped with an electron source, with ascanning means by which the surface of the sample placed on a samplemounting stage is to be scanned two-dimensionally using an electron beamemitted from the electron source, with a detection means for detectingthe electrically charged particles or electromagnetic waves releasedfrom the sample by the irradiation of the electron beam, and with anarithmetic unit which arithmetically measures the surface dimensions ofthe sample from the electrically charged particles or electromagneticwaves detected by the above-mentioned detection means, the presentinvention controls the scanning line interval within the scan area ofthe electron beam so that the irradiation density of the electron beamdoes not exceed the required value determined by the physicalcharacteristics of the sample.

Also, in order to achieve the above-mentioned second object, in themethod where a sample is to be scanned using an electron beam and thedimensions of the pattern formed on the sample are to be measured usingthe information obtained from the detection of an electron emitted fromthe scanned section, the present invention calculates beforehand thefunction that denote changes in the decreases of the above patterndimension, associated with the irradiation of the electron beam to thesample, and calculates the original dimensions of the pattern from thecorresponding function and from the length data obtained by the scanningof the sample with the electron beam.

Further details of the composition and effectiveness of the preventinvention are described in the section pertaining to the preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the scanning electron microscope shown asan embodiment of the present invention.

FIG. 2 is a view explaining the method of scanning with an electron beamduring the measurement of a line pattern dimension, subject to theprevent invention.

FIG. 3 is a view explaining the method of scanning with an electron beamduring the measurement of a hole pattern dimension, subject to theprevent invention.

FIG. 4 is a view explaining the outline of shrinkage due to the mutualaction between a photoresist and an electron beam.

FIG. 5 is a diagram showing the relationship between the number ofmeasuring operations and the amount of shrinkage.

FIG. 6 is a block diagram of the scanning electron microscope shown asanother embodiment of the present invention.

FIG. 7 is a view showing an example of a magnification selection screenmode.

FIG. 8 is a diagram showing the relationship between zeroth measureddata and actually measured data.

FIG. 9 is a diagram showing the calculation process for zeroth measureddata.

FIG. 10 is a diagram showing the relationship between the number ofmeasuring operations and the amount of shrinkage.

FIG. 11 is a diagram showing the process for calculating zeroth measureddata when impurities are present.

FIG. 12 is a view showing the outline of an input screen mode andmeasurement.

FIG. 13 is a diagram showing an internal interpolation process.

FIG. 14 is a diagram showing the measuring process for zeroth measureddata.

FIG. 15 is a flowchart showing the process in which an approximatefunction is to be stored into a memory beforehand and zeroth measureddata is to be calculated from the results of at least one measuringoperation.

FIG. 16 is a flowchart explaining the process for estimating zerothmeasured data from a previously calculated approximate function and fromthe optical conditions of the scanning electron microscope.

FIG. 17 is a flowchart showing the process for calculating thedifferences between zeroth measured data and (m+n−1)th measured data.

FIG. 18 is a flowchart showing the process for stopping lengthmeasurement when the required amount of shrinkage is observed.

FIG. 19 is a flowchart showing the preferred step in which, irrespectiveof pattern contamination, the approximate function that denotesshrinkage is to be accurately measured.

FIG. 20 is a diagram explaining the screen mode for selecting anapproximation scheme.

FIG. 21 is a diagram explaining a first example of the screen mode forselecting and supplying an approximation function.

FIG. 22 is a diagram explaining a second example of the screen mode forselecting and supplying an approximation function.

FIG. 23 is a diagram explaining a third example of the screen mode forselecting and supplying an approximation function.

FIG. 24 is a diagram explaining an example of the screen mode forsetting the optical parameters for the scanning electron microscope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of the scanning electron microscope shown as afirst embodiment of the present invention. A voltage is applied betweena cathode 1 and a first anode 2 by a high-voltage control power supply21 controlled by a control and arithmetic unit 30 (control processor),and the required emission current is induced from the cathode 1. Sincean acceleration voltage is applied between cathode 1 and a second anode2 by the high-voltage control power supply 21 controlled by the controland arithmetic unit 30, a primary electron beam 4 that has been emittedfrom cathode 1 is accelerated and then moves into the lenses arranged atthe succeeding stage. The primary electron beam 4 is converged by aconvergent lens 5 controlled by a focusing lens control power supply 22,and an unnecessary area is removed from primary electron beam 4 by adiaphragm plate 8.

After this, primary electron beam 4 is further converged as a micro-spoton a sample 9 through an objective lens 7 controlled by an objectivelens control power supply 23, and the surface of the sample is scannedtwo-dimensionally by a deflecting coil 11. The scanning signal from thedeflecting coil 11 is controlled according to the particular observingmagnification by a deflecting coil control power supply 24. Also, thesample 9 is fixed to the surface of a two-dimensionally movable samplestage 41. The movement of the sample stage 41 is controlled by a stagecontrol portion 25.

A secondary electron 10 that has been generated from the sample 9 by theirradiation of the primary electron beam 4 is detected by a secondaryelectron detector 12. A plotter 28 converts detected secondary signalsinto visible signals and controls these signals so that they arearranged as appropriate on another plane. Hereby, the imagecorresponding to the surface shape of the sample is displayed as animage thereof on a sample image display unit 26.

An input unit 27, which functions as the interface between the operatorand the control and arithmetic unit 30, and the operator controls eachof the above-mentioned units via the input unit 27 and specifiesmeasuring points and dimension measurement. A memory device not shown inthe figure is provided in the control and arithmetic unit 30 so as toenable storage of measured length data.

After being amplified by a signal amplifier 13, the signals that havebeen detected by secondary electron detector 12 are stored into theinternal image memory of the plotter 28. Although the apparatusaccording to this embodiment of the invention has a secondary electrondetector 12, the configuration of the apparatus is not limited hereby;either a reflected electron detector for detecting reflected electronsor a detector for detecting light, electromagnetic waves, or X-rays, canbe provided instead of or together with the primary electron detector.

The address signals corresponding to the memory locations within theimage memory are created in control and arithmetic unit 30 or in aseparately installed computer, and after undergoing analog conversion,the signals are supplied to deflecting coil 11. The address signals inthe X-axial direction are digital addresses whose values cyclicallychange in order from 0 to 512 in the case that the image memory formatis 512 pixels by 512 pixels, and the address signals in the Y-axialdirection are digital addresses whose values cyclically change in orderfrom 0 to 512 by being incremented by +1 when all values from 0 to 512are reached as the value of each address signal in the X-axialdirection. These signals are converted into analog signals.

Since linkage is established between the addresses within the imagememory and the addresses of the deflection signals for electron beamscanning, the original secondary image of the electron beam in thedeflecting area by the scanning coil is recorded in the image memory.The signals within the image memory can be sequentially read out inchronological order through a readout address creating circuitsynchronized with a readout clock. The appropriate signals that havebeen read out according to address are converted into analog form andbecome the brightness modulation signals of the sample image displayunit 28.

The image memory has a function that stores images (image data) inoverlapped (combined) form for improved S/N ratio. For example, theimages that have been obtained during eight two-dimensional scans arestored in overlapped form to form one complete image. In other words,the images that have been formed during one or more X-Y scans arecombined to form the final image. The total number of frame images forcreating one complete image can be arbitrarily set, and the appropriatevalue is usually set in consideration of conditions such as secondaryelectron generating efficiency. The desired final image can likewise beformed by overlapping a plurality of frame images on a plurality ofexisting frame images. Also, input of information to the image memorycan be interrupted by blanking the primary electron beam when storage ofthe desired number of images is completed or hereafter.

In addition, it is possible to provide a sequence in which, after thetotal number of frame images has been set to eight, when the ninth frameimage is acquired, the first frame image will be deleted and eight frameimages left as a result, or to provide weighted additive averaging inwhich, when the ninth frame image is acquired, the total number ofimages stored within the image memory is multiplied by a factor of ⅞ andthen the ninth frame image is added to the results.

The apparatus according to this embodiment of the invention also has afunction that forms a line profile, subject to the detected primaryelectron, the reflected electron, or the like. The formation of the lineprofile is based on either the quantity of electrons detected duringone-dimensional or two-dimensional scanning with the primary electronbeam, or luminance information relating to the image of the sample, andthe thus-obtained line profile is used for purposes such as measuringthe dimensions of the pattern formed on a semiconductor wafer.

During the measurement of a pattern dimension, two vertical orhorizontal cursor lines are displayed together with the sample image onthe sample image display unit 26, then the two cursors are placed at twoedges of the pattern via input unit 27, and the control and arithmeticunit 30 calculates the dimensions of the pattern from the informationconsisting of the sample image magnification and the distance betweenthe two cursors.

Although the description of FIG. 1 assumes that the control processoroperates integrally with the scanning electron microscope or by analogytherewith, the operation of the control processor is, of course, notlimited by the description and such processing as described below canalso be provided using a control processor provided independently of thescanning electron microscope. In that case, it is necessary to providetwo types of elements. One is a transmission medium for transmitting tothe control processor the signals detected by secondary electrondetector 12 or for transmitting signals from the control processor tothe lenses, deflector, and other components of the scanning electronmicroscope, and the other is input/output terminals for input and outputof the signals transmitted via the above transmission medium. Or aprogram that is to undertake processing described below can beregistered in a memory medium beforehand and then executed using acontrol processor provided with an image memory and capable of supplyingthe necessary signals to the scanning electron microscope.

In addition, the apparatus according to this embodiment of the inventionhas a function by which, for example, the section to be measured, theoptical conditions of the scanning electron microscope, and otherconditions for observing a plurality of points on a semiconductor arestored as a recipe beforehand and measurements and observations areconducted in accordance with the contents of the recipe.

Or a program that is to undertake processing described below can beregistered in a memory medium beforehand and then executed using acontrol processor provided with an image memory and capable of supplyingthe necessary signals to the scanning electron microscope. That is tosay, the embodiments of the present invention that are described beloware such that both embodiments are also established as the invention ofthe program which can be adopted for an electrically charged particleray apparatus such as a scanning electron microscope equipped with animage processor.

Embodiment 1

The shrinkage of the ArF photoresist pattern is likely to be caused bythe chemical reaction due to the convergent electron beam entering thephotoresist. The inventors have therefore performed experiments in orderto empirically derive the relationship between the acceleration voltageV_(acc) to the pattern of the convergent electron beam, electron beamcurrent density I_(pd), and the amount of shrinkage. As a result, 2S(the amount of shrinkage at both edges of a linear pattern in the casethat the amount of shrinkage at one edge is taken as S) has obeyedempirical formula (1).

2S=K1*V _(acc) ^(K2)·{1−exp(−(I _(pd) ^(0.5) ·n/K3))}  (1)

where 2S: the amount of shrinkage at both edges, V_(acc): theacceleration voltage (V), K1, K2, K3: parameters determined by thephotoresist, and n: the number of measuring operations. It can thereforebe seen that to suppress the shrinkage of the ArF photoresist pattern,associated with the irradiation of the electron beam, it is effective toreduce the electron beam irradiation density.

In this embodiment, in order to ensure highly accurate lengthmeasurement by suppressing such shrinkage of a sample that causeschanges in its shape due to electron beam irradiation as seen in the ArFphotoresist, the scan area on the sample surface is formed as a set ofmultiple scanning lines and when the shape and dimensions of the samplesurface are measured using either a straight line connecting thestarting and ending points of the dimension to be measured or thescanning distance of the convergent electron beam on scanning linesadjacent to the straight line, the scanning line interval can be set soas not to exceed such certain irradiation density value of the focusingelectron beam on the surface of the sample that is dictated by thephysical characteristics of the sample surface material.

In this embodiment, consideration is also given so that when themeasuring points are to be observed and when the field of view is to besearched for, the distance and interval of scanning lines at which theaspect ratio of the sample image becomes 1 to optimize the observationare set, and when measurements are to be performed, the scanning lineinterval is set so as not to exceed the above-mentioned certainirradiation density value on the surface of the sample, and so that as aresult, the scanning line interval during the measurements does notexceed the scanning line interval during the observation. That is tosay, for measurement, the ratio of the scanning line interval value withrespect to the length of the scanning lines is increased above the ratioto be applied to observation and to the search for the field of view.

In addition, the scan width of the scanning lines and the intervalthereof can be set for the conditions that minimize the amount ofshrinkage of the ArF photoresist pattern due to the electron beam, andafter combinations of these values have been registered as fixed valuesbeforehand, these combinations can be selected when measurements are tobe performed. Description is given below using drawings.

The method of electron beam scanning during pattern dimensionmeasurement in the present invention is shown in FIG. 2. FIG. 2( a) isfor a pattern of a linear shape. Under the prior art, for theobservation and measurement of a sample image, the length and intervalof the scanning lines are controlled so that the magnifications in thevertical and horizontal directions of the sample image take the samevalue with high accuracy, and for this reason, scans are conducted inthe square area shown as “a” in the figure. Under this method ofelectron beam scanning, however, as the micropattern size becomessmaller, since the image magnification must be increased to maintainmeasuring accuracy, this results in the electron beam scanning squarearea becoming smaller, thus increasing the electron beam irradiationdensity per unit area. Accordingly, for a sample whose physical andchemical changes are caused by the irradiation of the electron beam,such as a sample that suffers shrinkage as in the ArF photoresist, thereoccurs the problem that according to formula (1) shown above, theirradiation of the electron beam causes dimensional changes in thepattern and this prevents dimension data from being measured accuratelyor stably.

Next, the shrinkage of the ArF photoresist is described. Since theshrinkage of the ArF photoresist occurs when the electron beam that hasentered the photoresist collides with and are scattered about thephotoresist molecules, the shrinkage generally increases with increasesin the energy of the electron beam. Therefore, for the scanning electronmicroscope that measures the secondary electron generated from thesample, it is known that since the primary electron beam usually stopsinside the sample (in this case, the ArF photoresist), the shrinkagewill increase as the acceleration voltage of the primary electron beamincreases and as the quantity (current density) of electron beamsentering the ArF photoresist increases. In other words, since, even withthe same quantity of electrons, increases in measuring magnificationreduce the electron beam irradiation area, the quantity of electronsentering the same area correspondingly increases and shrinkageprogresses.

Next, the shrinkage of the photoresist due to its mutual action againstthe electron beam is outlined using FIG. 4. In FIG. 4 (1), the primaryelectron beam, after entering the ArF photoresist, repeats collidingwith and scattering about the photoresist over range R and then stops.In FIG. 4 (2), when electron beams enter one after another, thephotoresist area affected by the electron beams will shrink. However,not all the section affected by the electron beams will shrink. Instead,the shrinkage will occur only according to the rate of change of theparameter K1 determined by the photoresist. The new electron that hasentered will affect the photoresist that has shrunk, the photoresistthat has not shrunk even though it has been affected by the previouselectron, and a new photoresist that has not been affected by theprevious electron, and in this way, new shrinkage is caused. Thediscontinuous line in the figure denotes the position of the photoresistexisting before it shrunk. In FIG. 4 (3), the area where the shrinkageoccurred and the range of the electron beam have matched to terminatethe shrinkage.

In the prior art, although the shrinkage of photoresists due to theirradiation of electron beams has been achievable only by reducing thequantity of electron beams or the measuring magnification, there havebeen the problems that the S/N ratio of the secondary electron signaldecreases or that reduction in the magnification deteriorates measuringaccuracy and/or repeatability.

For these reasons, under the present invention, control and arithmeticunit 30 controls the scanning signal of the deflecting coil 11 by use ofdeflecting coil control power supply 24, and further provides control tomaintain the distance of scanning lines in a direction orthogonal to theline pattern to be measured (in the case of FIG. 2 (a), in the directionof the horizontal axis) while at the same time maintaining the imagemagnification in a horizontal direction, and to broaden the interval ofscanning lines in the direction of the line pattern (in the case of FIG.2, in the direction of the vertical axis) and thus reduce the imagemagnification in this direction, with the result that electron beamscanning occurs in the rectangular scan area shown as “b” in the figure.Hereby, since the electron beam irradiation density per unit area isreduced, changes in the dimensions of the ArF photoresist due to theirradiation of the electron beam are suppressed. This, in turn, not onlyenables highly accurate measurement of the dimension, but also enablesmeasurement without the deterioration of measuring accuracy since themagnification in the horizontal direction of the sample image does notdecrease.

At this time, the pattern the dimension can be calculated by arrangingtwo cursors at the secondary electron beam displayed on the imagedisplay unit and then performing arithmetic operations from the imagemagnification and the cursor-to-cursor distance by use of control andarithmetic unit 30. Or measurement data can be calculated by displayinga profile 20, which can be obtained by adding in a vertical directionthe profile of the horizontal signal intensity in the section existingbetween two horizontal cursor lines 19, and then detecting the edge ofthe pattern from the profile 20.

FIG. 3 shows electron beam scanning intended to measure a hole patternof a hole shape. For the prior art, a square scan area surrounding theintended hole is scanned with an electron beam and the hole pattern alsoneeds to be increased in image magnification according as the holediameter is reduced. This, in turn, increases the electron beamirradiation density, posing the problem that the photoresist shrinks.

Even in this case, under the present invention, control and arithmeticunit 30 controls the scanning signal of the deflecting coil 11 by use ofdeflecting coil control power supply 24, and further provides control tomaintain intact the distance of the horizontal scanning lines formeasuring the dimension on the image of the sample while at the sametime maintaining the image magnification in the horizontal direction,and to broaden the interval of scanning lines in a direction vertical tothe dimension measuring direction. Hereby, the electron beam irradiationdensity can be reduced and highly accurate measurements with minimumchanges in dimension can be performed without measuring accuracy beingaffected.

At this time, although the image shown in FIG. 3 (b) is formed byelectron beam scanning in the scan area mentioned above, it is allowedeither to arrange two cursors at the top of the elliptic image displayedon the image display unit and measure the diameter of the hole, or asshown in FIG. 3 (c), to detect the left and right edges in a multipointformat, then approximate the respective curves, and measure the holediameter at the position where the distance between the left and rightcurves becomes a maximum.

Another embodiment is possible. More specifically, although itsconfiguration is the same as that of FIG. 1, the distance and intervalof the scanning lines for observing the sample image and or searchingfor the measuring points can be set so that the magnification is thesame between the vertical and horizontal directions of the sample imageand so that only when measurement is specified from input unit 27 by theoperator, can the length and interval of scanning lines be set to valuessuitable for the sample and greater than the interval for observation.It is possible by doing so to supply the operator with a naturaloperating environment free from a feeling of uneasiness and to improvethe ease in operations.

Yet another embodiment is also possible. More specifically, although itsconfiguration is also the same as that of FIG. 1, when the sample to bemeasured is an ArF photoresist, the distance and interval of thescanning lines for the measurement can be set beforehand from theirradiation current value at which the shrinkage of the ArF photoresistbecomes a maximum.

The results of the experiments which have been conducted by theinventors by use of an ArF photoresist to represent the relationshipbetween the number of measuring operations and the amount of shrinkageare shown in FIG. 5. In the semiconductor manufacturing process thatuses an ArF photoresist, the line widths of patterns are limited to 0.1μm or less and to measure patterns of these line widths, imagemagnifications must be at least 100 k times as great. In this case, anacceleration voltage of 300 V and a probe current value of 4 pA are usedand the number of frames to be added is four. The horizontal andvertical magnifications of the sample image which can be measured inFIG. 5 without the deterioration of measuring accuracy during scanningbased on the prior art are 100 k times by look times, under whichconditions, the total amount of shrinkage which has occurred during 10measuring operations was about 4 nm.

Under the present invention, when the horizontal and verticalmagnifications of the sample image were set to 100 k by 49 k and 100 kby 30 k as the conditions for reducing the electron beam irradiationdensity by broadening the interval of scanning lines for a wider scanarea, the respective amounts of shrinkage were about 2.5 nm and 1.6 nm.

It can be judged from the above that when an ArF photoresist with a linewidth of 0.1 μm is to be measured, setting the horizontal imagemagnification to 100 k times and minimizing the electron beamirradiation density are preferable. Actual operation is also restrictedaccording to the vertical length of the pattern to be measured.

FIG. 6 shows yet another mode of embodiment, wherein control andarithmetic unit 30 is equipped with a memory unit 29 so thatcombinations of the optimal conditions for measuring the sample can bestored as fixed values. To the operator, there is the advantage thatmeasurements suitable for the sample can be easily performed within ashort time by selecting conditions from the combinations when measuringthe dimensions of the sample. FIG. 7 shows an example of a relatedselection screen mode, wherein the operator can easily performmeasurements in a new scan area by starting the measuring function afterselecting conditions suitable for the sample which is to be measured,from the combinations of fixed image magnifications that are displayedon the screen.

According to this embodiment of the invention, in the case of measuringsuch a photoresist that changes in shape by the action of the electronbeam irradiated for observing the sample, variations in shape can beminimized and highly accurate and stable measurement of the dimension ispossible.

Also, operational convenience improves since the observation of thesample and the search for the field of view of the section to bemeasured can be facilitated by selecting a normal square scan area forthe observation.

In addition, there is the advantage that since combinations of thescanning line length and interval matched to the characteristics of thesample are registered beforehand, the optimal measuring conditions canbe easily set by selecting the desired combination.

FIG. 24 is a diagram explaining an example of the screen mode forsetting the optical parameters for the scanning electron microscope. Inthis screen mode, it is possible to set at least the electron beamacceleration voltage (Accel. Volt), the probe current, themagnification, and the total number of frames (Frame#) necessary to formone frame image. Control and arithmetic unit 30 controls each opticalelement, subject to the data settings in the above-mentioned settingscreen mode. In the example of FIG. 24, data that can be set as theacceleration voltage, the probe current, the magnification, and thetotal number of frames, and actual data settings greater than the abovedata that can be set are displayed so as to be identifiable.

For example, for the selection of the total number of frames, aselection field consisting of permissible values such as 4, 8, 12, 16,24, and 32, is provided so that the operator can select the appropriatetotal number of frames. In the example of FIG. 24, although only 4 or 8can be selected from the above permissible values, the selection of 12,16, 24, 32, and so on up to the maximum permissible value is notaccepted.

For the apparatus pertaining to this embodiment of the invention, therequired value is set beforehand as the maximum amount of shrinkage andthere is also incorporated a sequence in which, when at least oneoptical parameter is set in accordance with formula (1), otherpermissible parameter data will be calculated and entry of data greaterthan the permissible parameter data will be inhibited. According to thisapparatus configuration, adequate observing conditions can be specifiedwith shrinkage reduced to its minimum.

Also, although an example of inhibiting entry of data greater than thepermissible parameter data has been explained in the description of theabove-described embodiment, this embodiment is not limited by theexplanation of the example. For example, if data greater than thepermissible parameter data is entered, the appropriate message can bedisplayed on the display unit or an audio warning can be issued. It isthus possible to notify to the operator that the settings of theremaining parameters are in excess of the respective required values.

Embodiment 2

For a semiconductor device, in order to achieve its design performance,the shape and dimensions of its circuit pattern requires stringentmanagement and for this purpose, a length-measuring electron microscopecapable of measuring micro-dimensions is used during their inspectionprocess. During observing and measuring processes, however, electronbeam irradiation for length measurement changes the shape of thepattern, as shown in FIGS. 4 (1) to (3). If this pattern is a linepattern, the length value measured will be smaller than the dimensionbefore it is measured, as shown in FIG. 8 (a). If the pattern is a holepattern, conversely, the length value measured will be larger than thedimension before it is measured, as shown in FIG. 8 (b), and this willcreate the problem that the dimension existing before shrinkage occurscannot be detected.

There is also the problem that when one section is continuouslymeasured, since line width is varied by the repetition of electron beamirradiation, different data measurement results are created with eachmeasuring operation and as a result, measuring accuracy does notimprove. Since the pattern shrinks according to length, the accuratedimension value of the pattern cannot be detected and this is a majorbottleneck in the semiconductor device manufacture that uses the ArFphotoresist.

The art disclosed in Japanese Application Patent Laid-Open PublicationNo. Hei 09-166428 is intended to reduce any effects of contamination onmeasurement by deriving approximate curves from a plurality of measuringoperations and then estimating the dimensions of the sample existingbefore electron beam irradiation. However, no consideration is given tothe fact that shrinkage progresses with an increase in the number ofmeasuring operations.

Also, at semiconductor factories, in order to evaluate the stability ofmeasuring equipment, one section is measured 10 times in succession andmeasured data is reduced in dispersion. However, since shrinkageprogresses according to the particular electron beam irradiation level,the repetition of length measurement at one point causes patternshrinkage, increases measured data in terms of dispersion (3σ: σ is thestandard deviation of measured data), and creates problems associatedwith process management.

In this embodiment of the invention, description is given of a lengthmeasuring method suitable for measuring the length of a pattern whoseshrinkage cannot be avoided, and an apparatus for conducting the lengthmeasurement.

As described earlier in this Specification, the shrinkage of the ArFphotoresist pattern is likely to be a chemical reaction due to theenergy of the convergent electron beam entering the photoresist. It canalso be seen from formula (1) that as the number of measuring operations(“n”) is increased, the amount of shrinkage (2S) will gradually decreaseand the shrinkage itself will eventually cease.

In addition, the measured data itself decreases with each measuringoperation and eventually converges to a fixed level at which theshrinkage does not progress any further. These changes in measuredlength data, plotted for the number of measuring operations, are shownin FIG. 9 (a), and it can be seen from FIG. 9 (b) that approximationwith the function of

is possible. This approximation function is a function showing how thepattern dimension changes (decreases).

Therefore, as can be seen from FIG. 9 (c), the dimensions of a patternbefore its shrinkage is caused by length measurement can be obtained bycalculating the approximation function from the length data that hasbeen obtained as a result of a plurality of pattern measurements, andthen providing the above approximation function with zero-pointextrapolation. The approximation function at this time can be of highorder or it can be a linear approximation function when the number ofmeasuring points is small. In the statement below, the estimated lengthvalue of the pattern before it shrinks is described as the “zerothvalue” in the meaning of the length value obtained by the zerothmeasurement based on the electron beam.

In this embodiment, in order to ensure measuring accuracy for suchsample suffering a change in shape due to electron beam irradiation asseen in the ArF photoresist, and achieve the objects described earlierin this Specification, the multiple length values that have beenmeasured at one measuring point using such a scanning electronmicroscope as set forth in FIGS. 1 and 6 are stored into a memory first.Next after an approximation function has been calculated from thesemeasured length values, the approximation function is extrapolated andthe dimensions of the ArF photoresist existing before an electron beamis irradiated are calculated.

Furthermore, up to now, the stability of a length measuring apparatus,especially, repeatability has been evaluated with 3σ, the dispersionbetween the length values that were obtained by repeating measurements10 times at one section. However, for such a sample deformed by electronbeam irradiation as in the ArF photoresist, measured length data varies,regardless of the characteristics of the length measuring apparatus.Consequently, the obtained 3σ value has not always indicated changes inthe characteristics of the length measuring apparatus.

In this embodiment, as shown in formula (2) below, after the firstzeroth length value (hereinafter, called the zeroth value) has beencalculated from an “m” number of length measurements, the (m+n)thmeasurement is performed and the second zeroth value is calculated fromthe (m+n) number of length data measurements. In this way, the thirdzeroth value, the fourth zeroth value, and so on up to the last zerothvalue are obtained from the (m+n) number of length data measurements,the (m+3) number of length data measurements, and so on up to the (n)number of length data measurements, respectively. Furthermore, theaccuracy of each of the zeroth values can be improved by setting “m” tothe appropriate value, and as measured data is chronologically newer,the magnitude of the data to be used for estimation will increase, withthe result that the zeroth values will improve in accuracy andreliability.

It is also possible, by enabling the evaluation of the dispersionbetween the 10 zeroth values which have thus been obtained, to improvemeasuring accuracy in comparison to evaluating the dispersion of thelength value itself which changes with each measurement, and thus toreduce the total dispersion. At this time, any number of zeroth valuescan also be selected to evaluate dispersion.

M _(0,1)=Fit(M ₁ , M ₂ , . . . M _(m))

M _(0,1)=Fit(M ₁ , M ₂ , . . . , M _(m) , M _(m+1))

. . .

. . .

. . .

M _(0,n)=Fit(M ₁ , M ₂ , . . . , M _(m) , . . . , M _(m+n−1))

where “M_(0, n)”, “M_(m)”, and “Fit( )” denote the nth zeroth value, themth measured length value, and the approximation function that has beenfitted to the selected value of all measured length data, respectively.

The desired zeroth value can be calculated from at least one measuringoperation by acquiring and storing into a memory beforehand theapproximation function that has been obtained above, and then using thisapproximation function when length is measured. Prior calculation of thefunction that denotes changes in the pattern dimension due to electronbeam irradiation makes it unnecessary to continue the electron beamirradiation for the calculation of the approximation function, and as aresult, damage to the pattern which shrinks can be minimized.

This approximation function can be selected from the multipleapproximation functions that have been calculated and registeredbeforehand for the sample which is to be measured. Or the amount ofenergy to be given to the sample under the current conditions duringmeasurement can be provided with internal interpolation from theacceleration voltage, the probe current, the observing magnification,the number of electron beam scans, and other approximation functionsthat have been calculated beforehand for the maximum/minimum electronbeam energy applicable to the sample, and these approximation functionscan be combined and the results can be used to estimate the zerothvalue. Once an actual length value has been obtained, the thus-obtainedapproximation functions are shifted horizontally for matching to theresults of one measuring operation, through such processes as shown inFIGS. 21 (a) to (c), and the zeroth value corresponding to the acquiredlength value is estimated.

With reference to the energy of the electron beam entering the sampleand variations in the shape and dimensions of the sample, since a changeof the acceleration voltage (V_(acc)) changes the energy itself of theelectron beam, an increase in V_(acc) also increases the energy appliedto the sample and, hence, variations in the shape and dimensions of thesample. Since increasing the current density (I_(p)) increases theirradiation current density and increasing the observing magnification(MAG) reduces the electron beam irradiation area inside the sample, theamount of current irradiation per unit area is augmented and the energyirradiated will also increase. Also, increasing the number of electronbeam scans (Frame) for an improved S/N ratio by increasing the quantityof signals from the surface of the sample increases the energy giventhereto in proportion to the number of scans.

Therefore, the approximation functions existing when the respectiveparameters are maximal/minimal are calculated beforehand and then theinternal interpolation matching to the particular length-measuringconditions is provided so that the zeroth values corresponding to eachparameter can be calculated. At this time, as shown in FIGS. 13 (a) to(c), the approximation functions for the maximum (P_(MAX)) values andminimum (P_(MIN)) values of parameters such as the acceleration voltagewhich can be applied to the sample, the current density, the observingmagnification, and the number of scans, are calculated and stored into amemory beforehand, and then the approximation functions obtained byinternally interpolating each such parameter for each measuringoperation are combined to obtain the approximation functioncorresponding to the current irradiation energy. The thus-obtainedapproximation function is shifted horizontally in the axial direction ofmeasured length data in FIG. 13, then matched to the results of onelength measurement, and the zeroth data corresponding to the irradiationenergy is estimated. The above optical parameters can be arbitrarily setfrom, for example, input unit 27, and control and arithmetic unit 30controls each optical element of the scanning electron microscope inaccordance with the instructions sent from input unit 27. Electron beamscanning can be either one-dimensional or two-dimensional.

By the way, as shown in formula (3), the final variation in the volumeof the sample “Δ_(total)” can be calculated and output as the differencebetween the zeroth value and the final measured value by calculating thezeroth value from the approximation function.

Δ_(total) =M _(0,T) −M _(m+T−1)  (3)

where M_(0, T) and M_(m+T−1) denote the final zeroth value and measuredlength value, respectively. Furthermore, as shown in formula (4), thedifference Δ_(n) between the nth zeroth value M_(0, n) and the (m+n−1)th measured length value M_(m+n−1) can be calculated each time ameasuring operation is performed.

Δn=M _(0,n) −M _(m+n−1)  (4)

Or instead of calculating variations as shown above, it is possible tocontinuously execute length measurement at one measuring point withrespect to the variation X in any sample volume that was entered fromthe input unit, and continue the measuring process until the Δ shown informula (4) above has overstepped the range of X. That is to say,formula (5) can be added as a measuring condition.

|Δ_(n)|<X  (5)

When calculated |Δ_(n)| exceeds X, he measuring process will beterminated, and the calculated zeroth data, dispersion 3σ betweenmeasured data, variation Δ in the volume of the sample, and a graphshowing changes in these parameters will be displayed. It is alsopossible to select not only Δ, but also other parameters (for example,dispersion 3σ between measured data), as the parameters in formula (5)above.

Although the electron microscope is an apparatus that irradiateselectron beams from its vacuum vessel to the sample to be measured, itis known that if the molecules of a carbon polymer or of othersubstances are present in the vacuum vessel, these molecules will reactwith the sample and accumulate as impurities (hereinafter, called“contamination”) on the sample when electron beams are irradiated. Inthe present invention, since length measurement is continuously executedat one measuring point, when electron beam irradiation is continued evenafter the shrinkage of the ArF photoresist has ceased, length datameasured subsequently will increase according to the quantity ofcontamination proportional to the electron beam irradiation energy.

When measurements are continuously performed at one measuring point, thegradient (K_(s)) of the linear component is calculated as in formula (6)after the tendency of measured data to increase has been confirmed. Thequantity of contamination which has stuck to the sample during themeasuring process at up to that time can be calculated using formula(7).

K _(s)=(M _(r) −M _(n))/(r−n)  (6)

C=K _(s) ·r  (7)

where “r”, “n”, “C”, “M_(r)”, and “M_(n)” denote the number of measuringoperations, the number of measuring operations in which the shrinkageceased, the quantity of contamination which has stuck to the sample, therth measured value, and the nth measured value, respectively. Whetherthe tendency of measured data has changed to an upturn can be judged asfollows. That is to say, the rth measured value and the average(“M_(ave, r)”) of all data down to the (r−5)th measured value arecalculated and stored into a memory. The rth measured value is comparedwith the previous average value of (“M_(ave, r−1)”) to confirm thedifference between both values. If comparison results indicate aplurality of times in succession that the rth measured value is greater,the shrinkage of the photoresist will be judged to have ceased, as shownin FIG. 11 (a). The data section that has increased is estimated to bedue to the contamination of the carbon-based substances linearlysticking to the sample during the electron beam irradiation. For thisreason, the gradient (K_(s)) of the increase section in the graph iscalculated, then after, as shown in FIG. 11 (b), the value (M_(m)′)obtained by subtracting the linear component from the measured data“M_(m)” has been calculated and memory-stored, the approximationfunction allowing for the quantity of contamination is calculated, andit therefore becomes possible to calculate the zeroth value (M_(0, n)″),dispersion between measured data, a variation (Δ) in the volume of thesample, and the like, from the above results and thus to performmeasurements with even higher accuracy.

M _(m) ′=M _(m) −K _(s) ·m  (8)

M _(0,n)″=Fit(M ₁ ′, M ₂ ′, . . . , M _(m+n−1)′)  (9)

Δ″=M _(0,n) ″−M _(m+n−1)′  (10)

This embodiment of the invention is described in detail below usingflowcharts.

As shown in FIGS. 8 (a) and (b), for pattern dimension measurement, twovertical cursor lines 18 or two horizontal cursor lines 19 are displayedtogether with an image of the sample on the sample image display unit26, then the two cursors are placed at the edges of two sections on thepattern via input unit 27, and control and arithmetic unit 30 calculatesthe measured data as the dimension data of the pattern, from theinformation consisting of the image magnification of the sample imageand the distance between the two cursors, and stores the results intothe memory unit. After length measurement has been continuouslyrepeated, sequential calculation results on measured data are storedinto the memory unit and the approximation function is calculated bycontrol and arithmetic unit 30. Control and arithmetic unit 30calculates the zeroth data from this approximation function inaccordance with formula (2) and stores the results into the memory unit.The calculated zeroth data can also be displayed on sample image displayunit 26.

Length measurement results on the line pattern of the ArF photoresistdealt with in the present invention, and related zeroth data are shownin FIG. 8. Originally, before electron beams are irradiated, the patternwidth shown as the “zeroth value” in FIG. 8 (1) is measured as theafter-measurement width in FIG. 8 (2) from the line profile within therange specified by the horizontal cursor lines 19 of the line pattern,since the irradiation of the electron beam causes the ArF photoresist toshrink and the line profile to change.

Further details of this embodiment are described below using theconceptual diagram of FIG. 9 in line with the flow diagram of FIG. 14.In step 1411, the length of the intended pattern on the sample ismeasured, and in step 1412, the measured value is stored into the memoryunit. The value at this time is stored as the value corresponding to thefirst measuring point (M₁) in FIG. 9 (a). Following this measuringoperation, the measuring process is repeated at the same measuringpoint, and the respective measurement results are stored as measuredlength values M₂, M₃, and so on up to M_(m). As shown in FIG. 9 (b), themeasured length data approximation functions with respect to the numberof measuring operations is calculated from the “m” number of lengthmeasuring points for an “m” number of length measurements by control andarithmetic unit 30 (FIG. 9 (b) shows an example of approximation with aquartic formula, and in FIG. 14, “m” is taken as 3). Next as shown inFIG. 9 (c), the zeroth value M_(0,1) is calculated by providing thezeroth measurement with extrapolation and the results are memory-stored.When the length measuring process is further continued, approximationfunctions are sequentially calculated from an (m+1) number of measuringpoints, an (m+2) number of measuring points, and so on up to an (m+n−1)number of measuring points, in step 1413, and the zeroth data iscalculated and stored. Following completion of the length measuringprocess in step 1414, an “n” number of zeroth values, approximationfunctions, data dispersion (3σ), and other data will be displayed ondisplay unit 26 in step 1416.

Also, ten zeroth values are calculated by the arithmetic unit similarlyto the above. After this, the standard deviation σ is derived from theten calculated zeroth values M_(0, 1), M_(0, 2), M_(0, 3), and so on upto M_(0, 10), and 3σ, which is obtained by multiplying σ by three, iscalculated and displayed as an index denoting the stability of thelength measuring apparatus. Thus, data on the stability of the lengthmeasuring apparatus can be calculated and displayed without beingaffected by changes in the volume of the sample due to electron beamirradiation. The calculation of the standard deviation from thethus-obtained zeroth values enables the accuracy of the apparatus to beeasily confirmed when length measurements are performed on suchmicropatterns (100 nm or less) as formed by the photoresist reacting toargon fluoride (ArF) eximer laser light.

Next, an example of storing approximation functions beforehand andcalculating zeroth values from the results of one length measuringoperation is shown below using the flow diagram of FIG. 15.

In cases such as conducting automatic length measurements on a pluralityof samples using a length measuring electron microscope and one recipe,the approximation functions that were obtained similarly to theabove-described embodiment are stored beforehand in step 1509, then thezeroth value M_(0, 1), is calculated from the results of one lengthmeasuring operation that were obtained in step 1502, by providingcorrections using the above-mentioned approximation functions, as shownin FIGS. 21 (a) to (c), and the results are stored into the memory unitin step 1505. After the lengths of the multiple samples have beenmeasured, dispersion 3σ between the zeroth data, which is themeasurement results, is calculated and stored in step 1507 and thezeroth values and data dispersion of each sample are displayed ondisplay unit 26. The data at this time can be displayed with eachcalculation of the zeroth value. Also, the approximation functions usedcan be such that as shown in step 1509, they have been acquiredbeforehand using one sample, or such that as shown in step 1501, theyhave been obtained in the range of automatic length measurement. It ispossible, by adopting such composition, to calculate zeroth values withat least one measuring operations and thus to minimize the shrinkage ofthe pattern whose length is to be measured.

Next, an example of zeroth data estimation based on the approximationfunctions that have been calculated beforehand, and on the opticalconditions of the electron microscope, is described using the flowdiagram of FIG. 16. In the case of automatic length measurement of aplurality of samples by use of a recipe, in step 1609, the approximationfunctions P_(max) and P_(min) obtained when the parameters for changingthe energy of electron beams to be applied to each sample (namely,acceleration voltage: V_(acc), current density: I_(p), measuringmagnification: MAG, and the number of electron beam scans: Frame) aremaximal and minimal are calculated by control and arithmetic unit 30 andcalculated data is stored into the memory unit. Since the data variesfrom sample to sample in terms of the type of photoresist material andthe shape of the pattern, data matching the type of sample needs to beacquired and stored and the appropriate data for the intended sample isto be selected from acquired and stored data.

Measured length value M₁ is acquired and stored in step 1601, then instep 1603, the approximation functions obtained during one lengthmeasuring operation when the P_(max)-P_(min) section is internallyinterpolated are, as shown in FIG. 13 (b), calculated from the currentparameter status and stored by control and arithmetic unit 30. Afterthis, as shown in FIG. 13 (c), the calculated and stored approximationfunctions are further combined and stored as the approximation functionsfor the estimation of zeroth data.

When the current irradiation conditions are maintained in the lengthmeasuring process, correction coefficients can be calculated by checkingthese coefficients against the length measuring energy conditions eachtime the measurement is conducted, or the coefficients that have thusbeen calculated can be used to calculate zeroth value M_(0, 1) duringsubsequent measuring operations. After that, in step 1604, approximationfunctions are calculated from the measured length data that has beenstored into the memory unit, and the approximation function obtained bycombining the calculated and stored approximation functions is shiftedhorizontally with respect to each measured length value, as shown inFIGS. 20 (a) to (c). Hereby, the zeroth value M_(0, 1) obtained bycorrecting the quantity of energy irradiation to the sample iscalculated and stored.

After all sample length measurements have been completed, dispersion 3σbetween a plurality of zeroth values M_(0, 1) is calculated in step 1607and the plurality of zeroth values M_(0,1) and the dispersion 3σ betweenthese values are displayed on display unit 26 in step 1608. Ifnecessary, the display can be made each time a zeroth value is acquired.Data acquisition in step 1609 can take place in an earlier step orimmediately before step 1601.

It is possible, by adopting the composition described above, tocalculate the approximation functions matching the optical parameters,and thus to select the appropriate approximation function even after theapparatus conditions have been modified.

In this embodiment of the invention, such input unit as shown in FIGS.21 to 23 is provided to enable the operator to arbitrarily acquire andset, or to edit, the approximation function to be used for measurement.

In the input screen mode shown in FIG. 21, the operator can selectwhether the approximation functions that have been acquired beforehandare to be used to estimate zeroth values, or whether the approximationfunctions that have been automatically calculated for the incidentenergy to the sample. Also, the input screen mode shown in FIG. 22enables the acquisition not only of the approximation functions thathave been acquired beforehand, but also of new approximation functions.In addition, the approximation curves separately supplied from theapparatus supplier, manufacturer, and/or the like, can be introduced andthese curves can be edited and selected to estimate zeroth data.

Furthermore, in the screen mode of FIG. 23, not only the approximationfunctions to be used to estimate zeroth data, but also the approximationcurves obtained when the acceleration voltage, the electron beamdensity, the observing magnification, the number of electron beam scans,and other parameters required for automatic zeroth data estimation fromthe incident energy level are maximal and minimal can be supplied fromthe apparatus supplier, manufacturer, and/or the like.

FIG. 17 is a flowchart showing the process for calculating thedifference between the zeroth value and (m+n−1)th measured length value.In steps 1701 to 1704 of FIG. 17 (a), measurement at one measuring pointis repeated (m+T−1) times, then after approximation functions have beencalculated, zeroth data is calculated. Next in step 1705, by use offormula (3), the total variation “Δ_(total)” in the (m+T−1) number ofmeasurement results is calculated from the zeroth value M_(0, T) thathas been calculated from the (m+T−1) number of measured length values,and from the (m+T−1)th measured value M_(m+T−1), and calculation resultsare stored.

In step 1706, the variation “Δ_(total)” is displayed on display unit 26.At this time, the degree of shrinkage can be easily understood by, asshown in FIG. 17 (b), calculating and displaying the difference “Δ_(m)”between the (m+n−1)th zeroth value M_(0, n) and the (m+n−1)th measuredlength value M_(m+n−1), during each length measuring operation by use offormula (4).

FIG. 18 is a flowchart showing the process for stopping the lengthmeasuring process when the required amount of shrinkage is detected orwhen the dispersion in zeroth data decreases below the required value.In step 1801, by use of such input screen mode as shown in FIG. 12 (a),the operator can select either the dispersion 3σ of any measured lengthdata or the variation “Δ” in the volume of the sample, and enter a valueof X. Subsequently, in steps 1802 to 1804, the current zeroth valueM_(0, n) is calculated from the calculated and stored length data thatwas continuously measured at one measuring point, and then in step 1805,dispersion 3σ or the variation “Δ_(n)” in the volume of the sample iscalculated. In step 1806, it is judged using formula (5) or (11) whetherthe calculated 3σ decreases below the required value or whether thevalue of “Δ_(n)” exceeds the X value that was entered in step 1501.

3σ<X  (11)

As shown in FIG. 12 (b), when the absolute value of the calculated 3σ or“Δ” exceeds the entered X value, the length measuring process will becompleted, and in step 1808, the calculated zeroth value M_(0, n), 3σ or“Δ_(n)” value, and a graph that shows changes in these values aredisplayed on display unit 26. If X is not exceeded, the length measuringprocess will be terminated in step 1807 and the finally obtained “N”number of zeroth values M_(0, N), 3σ or “Δ_(N),” value, and a graph thatshows changes in these parameters are displayed.

A sufficient number of scans for achieving the required measuringaccuracy can be set by configuring the apparatus in such a manner thatas set forth above, the length measuring process will be stopped whenthe required variation is detected or when the dispersion of zeroth datadecreases below the required value. Since the amount of shrinkagegreatly depends on the type of photoresist, it is difficult to find thenumber of measuring operations that is required for the achievement ofthe required measuring accuracy. According to the present embodiment,however, data setting for achieving the required zeroth data detectionaccuracy can be easily implemented, irrespective of the type ofphotoresist. Also, throughput improves since the appropriate number ofmeasuring operations can be set.

Although, in the embodiment of FIG. 18, management based on the numberof measuring operations (the number of scans) occurs, this does notlimit the embodiment; it is also possible to provide control so thatelectron beam scanning is interrupted after the amount of shrinkage hasbeen chronologically managed on a unit time basis and the required timeof electron beam scanning has been executed.

FIG. 19 is a flowchart showing the preferred steps for accuratelymeasuring the approximation functions which denote shrinkage,irrespective of contamination sticking to the pattern. In step 1901,length measurements are continuously performed at one measuring pointand measured length data is calculated and stored. In step 1902, theaverage (“ave,r”) of all data from the (r−5)th measured value to the rthmeasured value is calculated and stored and the difference “M_(diff, r)”from the average of all data from the (r−6)th measured value to the(r−1)th measured value is calculated and stored. In step 1904, after thedifference “M_(diff, r)” has become plus a plurality times insuccession, shrinkage stops, then the measured length data is judged tohave begun linearly increasing, and the length measuring process isterminated, as shown in FIG. 11 (a). After this, in step 1905, thegradient K_(s) of the linear component is calculated using formula (6).Since the linear component represents the contamination sticking to thesurface of the sample, the quantity of contamination which has stuck canbe calculated using formula (8).

Even during the shrinkage of the sample, contamination sticks accordingto the particular number of measuring operations. For this reason, instep 1906, the value obtained by subtracting the linear component frommeasured length value M_(m) is calculated as the measured length valueM_(m)′ which allows for the quantity of sticking contamination, byapplying formula (8) to all the measured length values that were storedinto the memory unit. In step 1907, all approximation functions from M₁′to M_(m)′ are newly calculated and then the zeroth values M_(0, n)″obtained by providing linear component correction using formula (9) arecalculated and stored. In addition, the calculation of the variation Δ″in the volume of the sample existing after linear component correctionusing formula (10) has been provided, and the calculation of thedispersion 3σ″ between zeroth values M_(0, n)″ obtained by providinglinear component correction are performed and then in step 1908, thezeroth values M_(0, n)″ obtained by providing linear componentcorrection, the dispersion 3σ″, the variation Δ″ in the volume of thesample, the newly calculated approximation functions, and other data aredisplayed on display unit 26. Even if contamination sticks, accurateapproximation functions can be obtained by adopting the compositiondescribed above.

As set forth above, according to the present embodiment of theinvention, during the measurement of such a photoresist, which uses anargon fluoride (ArF) eximer laser as its light source, that changes inshape by the action of the electron beams irradiated for the observationof the sample, the length of the pattern existing before a change inshape occurs can be measured in at least one measuring operation andhighly accurate dimension measurement is possible. Automatic lengthmeasurement is also possible and dispersion in measured data can bereduced. In this context, there are advantages associated with processmanagement of semiconductor manufacture.

In addition, automatic measurement of variations in the volume of thesample with respect to the quantity of electron beam irradiation becomespossible and a graph of changes can be displayed on the screen. These,in turn, facilitate the examination of the optimal electron beamirradiation conditions for ArF photoresist measurement, and offers anadvantage associated with the management of the pattern width during theuse of an electron beam apparatus such as a length measuring electronmicroscope.

Furthermore, it becomes possible to obtain the measured length dataexisting before the shape of the sample changes, even when stickingimpurities are present on the surface of the sample, and to conducthighly accurate dimension measurements.

1.-8. (canceled)
 9. A sample dimension measuring method in which thedimensions of the pattern formed on a sample are measured by scanningsaid sample with electron beams and detecting the electrons releasedfrom the scanned section, wherein the dimension measuring method ischaracterized in that the functions that denote such changes in the rateof decrease of said pattern dimension that occur when electron beams areirradiated to the sample are calculated beforehand and in that thedimensions of the pattern existing before it dimensionally decreases areestimated from said functions and the length data obtained by scanningthe surface of the sample.
 10. A scanning electron microscopecomprising: an electron source, a deflector for scanning with theelectron beams which are emitted from said electron source, a detectorfor detecting the electrons released from a sample by said electron beamscans, and a control processor for measuring the dimensions of thepattern on said sample in accordance with the output of said detector,wherein said control processor has a memory unit into which thefunctions that denote such changes in the rate of decrease of saidpattern dimension that occur when electron beams are irradiated to saidsample can be stored, and wherein the dimensions of the pattern existingbefore it dimensionally decreases are calculated from the storedfunctions mentioned above and the length data obtained by scanning thesurface of the sample.
 11. The scanning electron microscope as set forthin claim 10 above, wherein more than one function denoting such changesin the rate of decrease of said pattern dimension is stored within saidmemory unit.
 12. The scanning electron microscope as set forth in claim11 above, wherein said functions are stored inside said memory unit foreach optical parameter of the scanning electron microscope.
 13. A sampledimension measuring method in which the dimensions of the pattern formedon a sample are measured by scanning said sample with electron beams anddetecting the electrons released from the scanned section, wherein thedimension measuring method is characterized in that after said samplehas been scanned with electron beams a plurality of times, then aplurality of values have been detected as changes in measured dimensionvalue, and more than one approximation function denoting changes in thethus-obtained dimension measurement results has been calculatedchronologically or for each said electron beam scan, the dimensions ofthe pattern existing before electron beams are irradiated thereto areestimated from said multiple approximation functions a plurality oftimes and then the number of electron beam scans or scanning time formeasuring said pattern dimension is determined from the number of scansat which, or the timing in which, the estimated pattern dimensionbecomes a dispersion value smaller than the required value.
 14. A sampledimension measuring method in which the dimensions of the pattern formedon a sample are measured by scanning said sample with electron beams anddetecting the electrons released from the scanned section, wherein thedimension measuring method is characterized in that a plurality ofvalues are detected as changes in measured dimension value, then afterthe approximation functions that denote changes in the thus-obtaineddimension measurement results have been calculated and said changes inthe dimension have decreased below the required value, said electronbeam scans are stopped and the dimensions of the pattern existing beforeelectron beams are irradiated to said pattern are calculated.
 15. Ascanning electron microscope comprising: an electron source, a deflectorfor scanning with the electron beams which are emitted from saidelectron source, a detector for detecting the electrons released from asample by said electron beam scans, and a control processor formeasuring the dimensions of the pattern on said sample in accordancewith the output of said detector, wherein said control processor has ameans for setting at least one of four parameters, namely, themagnification, the acceleration voltage, the number of measuringoperations, and the probe current, and a memory unit into which thefunctions that denote such changes in the rate of decrease of saidpattern dimension that occur when electron beams are irradiated to saidsample can be stored, in that said functions are converted in accordancewith at least one value that has been set using said setting means,namely, either the magnification, the acceleration voltage, the numberof measuring operations, or the probe current, and in that thedimensions of the pattern existing before electron beams are irradiatedto said pattern are calculated from the converted functions mentionedabove.
 16. A sample dimension measuring method in which the dimensionsof the pattern formed on a sample are measured by scanning said samplewith electron beams and detecting the electrons released from thescanned section, wherein the dimension measuring method is characterizedin that a plurality of values are detected as changes in measureddimension value, then after the functions that denote changes in thedimensions of the pattern and the functions that denote increases in thepattern dimension which decreased have been calculated, the functionsthat denote said decreases are corrected for using the functions thatdenote increases, and the dimensions of the pattern existing beforeelectron beams are irradiated to said pattern are calculated.